Police are investigating after an 11-year-old girl was found dead at a sleepover Wednesday.

The girl, who has not been identified, was playing with her iPad around 1:30 a.m. before falling asleep, a friend of the victim told police, according to WPVI.

Later that morning, she was found unresponsive, according to WPVI. An autopsy will be conducted next week.

"With the age of the victim, there was a concern right away," Philadelphia police Lt. Dennis Rosenbaum told WCAU. "We are taking all the investigative steps."

The girl frequently stayed the night at the house, which is just a couple doors down from where she lived, according to WCAU.

Investigators are unsure what happened. They think she could have had an unknown condition or a food allergy, according to WPVI.